It has conventionally been known that a smear phenomenon occurs when a bright object is captured with a pixel array in which a plurality of pixels (photodiodes) are arrayed in the row and column directions, and the captured signal is transferred by a CCD (Charge Coupled Device). More specifically, an unwanted signal component generated by photoelectrically converting light corresponding to a bright object by pixels is mixed in a photoelectrically converted image signal transferred via a vertical transfer path. An image obtained from this image signal contains a vertical white streak, that is, smear region in the column direction of the pixel array (see FIG. 7). The luminance level of pixels in the smear region becomes higher than an actual luminance level.
When the photometry target includes a bright object, an image containing a smear region is obtained, and the exposure value is obtained using the image, underexposure may occur in actual photographing. To prevent this, according to a technique disclosed in Japanese Patent Laid-Open No. 5-007335, the smear amount of pixels in the smear region is detected from a signal obtained by performing idle scanning (scanning before photometry) without reading out any signal from photodiodes before photometry. Then, photometric scanning is done to acquire an image signal (by reading out signals from the photodiodes), and the detected smear amount is subtracted from the image signal, obtaining an image signal in which the smear region is corrected. Then, the exposure value is obtained using the corrected image signal. This can prevent underexposure in actual photographing.
The technique disclosed in Japanese Patent Laid-Open No. 5-007335 requires an extra period for performing scanning before photometry, so the frame period for capturing a 1-frame image may become long. When a moving image for EVF display on the display unit is captured, images which lose the continuity of operation may be obtained.
To prevent this, the smear amount is detected by an OB (Optical Black) portion arranged on the lower side of the pixel array, as shown in FIG. 7. In this case, the smear amount can be detected without setting an extra period for performing scanning before photometry. FIG. 7 shows the pixel array, the OB portion, and an image obtained by them, which are superposed on each other. The OB portion extends in the row direction of the pixel array.
Assume that a bright object stands still. In this case, the signal of a smear component detected in the row direction of the pixel array is extended in the column direction to estimate a corrected region CR1 as a smear region. Smear correction is performed by subtracting the smear amount of the corrected region CR1 as a correction amount from image data generated by capturing the object with the pixel array. At this time, the corrected region CR1 coincides with an actual smear region SR1.
Assume that a bright object moves in the row direction (lateral direction). In this case, as disclosed in Japanese Patent Laid-Open No. 6-268922, the smear region extends obliquely in an image obtained by capturing the object (see FIG. 8). The signal of a smear component detected in the row direction of the pixel array is extended in the column direction to estimate a corrected region CR2 as a smear region. Smear correction is performed by subtracting the smear amount of the corrected region CR2 as a correction amount from image data generated by capturing the object with the pixel array. At this time, the corrected region CR2 is shifted from an actual smear region SR2. In the corrected region CR2 and smear region SR2, only overlapping regions SR2a and CR2a are properly corrected, generating a false corrected region CR2b and uncorrected region SR2b. The luminance level of the false corrected region CR2b is lower than that of peripheral pixels by the correction amount.
As described above, when smear correction is done for image data generated by capturing a moving bright object, an image containing a black streak in the vertical direction is obtained. The contrast of the black streak with peripheral pixels is high, degrading the quality of an image to view.
The black streak can be made less conspicuous in the image by setting the correction amount to less than 100% (e.g., 50%) of the smear amount of the corrected region CR2. However, the smear component still remains. Thus, if control operations such as exposure control, focus adjustment, and white balance control are executed using this corrected image data, the precision of the control operations may decrease.
For example, when the exposure value is obtained using smear component-containing image data, underexposure may occur in actual photographing.
For example, when the focus state is detected using smear component-containing image data, the focus may be adjusted to a position where not the contrast of the object but that of the edge of the smear amount is maximized.